The physiological mechanisms of fibrinolysis are regulated by vascular plasminogen activator and α2-plasmin inhibitor. The vascular plasminogen activator and plasminogen are adsorbed to fibrin, and plasminogen activation takes place on the surface of fibrin. This efficient mechanism of fibrinolysis is inhibited by α2-plasmin inhibitor which interferes with the adsorption of plasminogen to fibrin. The blood level of α2-plasmin inhibitor as well as the production and release of vascular plasminogen activator from blood vassels take determinant roles in the whole process of physiological fibrinolysis.